In Phase 1, measuring and characterizing glucose oscillations in yeast cells immobilized on the surface of a glucose sensor was completed. Using this as a model, it was postulated that within the subcutaneous environment, cells (e.g., fibroblasts, adipocytes) would be in close proximity to the surface of the glucose sensor thereby mimicking the in vitro environment of the yeast cells on the surface of the glucose sensor. A 12- hour clinical study was completed wherein glucose measurements within interstitial fluid were highly correlated with reference glucose measurements. Moreover, measurements of glucose oscillations within subcutaneous tissue showed clear differences between normal subjects and those with type 1 and type 2 diabetes. Further studies in Phase 2 are aimed at building a data base of measurements, over longer time periods, to provide the means for characterizing different states of glycemia along the continuum from normal to impaired glucose tolerance to type 2 diabetes. Information gained from human studies in Phase 2, could provide the means of controlling an insulin pump based on periodic changes in cellular glucose metabolism, rather than relying solely on peripheral fingerstick blood glucose measurements for calibration purposes. Continuous glucose monitoring is an evolving, revolutionary technology that promises to improve the quality of life for millions of people with diabetes. In order to realize its full potential, more accurate devices that can be used for diagnosis and control, by providing physiological feedback to an insulin pump, are required. Measuring subcutaneous metabolic oscillations of glucose could provide a missing link for insulin pump feedback control, more accurate glucose measurements and novel methods for diagnosing stages of impaired glucose tolerance and insulin resistance. Measuring and characterizing aberrations in glucose metabolism within interstitial fluid and correlating them to known defects in glucose metabolism could be a major leap forward in diabetes management and provide an inexpensive tool for discovering new insights into the genetic and molecular origins of insulin resistance. The proposed Phase 2 research may result in a CGM system that reduces the need for frequent fingerstick blood glucose re-calibration eventually leading to a user calibration-free CGM that can be interfaced with an insulin pump to form an artificial pancreas.

Public Health Relevance

The potential for continuous glucose monitoring systems (CGMs) to detect cellular glycemic oscillations in interstitial fluid will advance the use of CGM technology into the realm of preventative medicine by providing an inexpensive screening tool, capable of identifying people with abnormal glucose metabolism long before overt clinical symptoms are apparent. In addition, our proposed research seeks to advance the state-of-the-art in continuous glucose monitoring by developing a convenient and useful method for evaluating glycemic control over shorter periods of time (days or weeks) that could potentially supplement quarterly assessments of glycemic control using hemoglobin A1C measurements. The measurement of subcutaneous glucose oscillations could lead to better control of an insulin pump based on cellular feedback as opposed to current CGM technologies that require frequent re-calibration using fingerstick glucose monitoring.